1. Field
Embodiments of the present technology relate to gas valves for use in gas appliances. More particularly, embodiments of the technology involve a variable gas valve for modulating a flow of gas into a burner of a gas appliance.
2. Description of Related Art
Gas valves are used to regulate an amount of gas fed to a gas appliance such as, for example, an oven, furnace, hot water heater, or fireplace. Gas valves have traditionally had two settings, on and off. Use of such valves causes undesirable fluctuations in appliance output. An oven set at 350° for example, may fluctuate between 345° and 355° as the oven temperature control cycles through on at 345°, off at 355°, and then back on at 345°.
To address the problem of output fluctuation in gas appliances, variable gas valves were developed to modulate gas flow across a range of outputs instead of between an on position and an off position. Such variable gas valves enable output control systems to operate with less fluctuation than a traditional on/off type gas valve.
U.S. Pat. Nos. 6,968,853; 6,029,705; and 5,979,484 all provide gas flow modulation by regulating the pressure of the fuel supplied to a fixed orifice. However, this method of gas flow modulation inherently causes a significant drop in pressure ahead of the orifice, resulting in a decrease in the velocity of the gas exiting the orifice, thus reducing the amount of primary air in atmospheric type burners, which negatively impacts the quality of flame and amount of complete combustion at the burner, increasing the volume of non-combusted materials in the flue gases exhausted to the atmosphere.
U.S. Pat. No. 4,930,488 provides a solenoid operated microprocessor-actuated modulating gas valve, operating in a similar manner as above by restricting flow between a poppet and outlet seat. However, even though this valve does include the outlet orifice on the valve, the flow restriction occurs at the outlet seat, thereby reducing the pressure to the fixed orifice.
U.S. Pat. No. 5,458,294 provides a variable orifice solenoid operated valve as a control device to meter gas flow as a function of sensed temperature and desired temperature. However, this design exhibits an undesirable amount of hysteresis and non-repeatability during operation depending on the particular sequence, length and direction of setting adjustments.
U.S. Pat. Nos. 5,249,773; 3,402,739; 3,090,423; and 3,084,865 all provide a gas valve employing a metering pin operating at the outlet orifice as a method of modulating the fuel flow into the burner. These type modulating valves overcome the aforementioned problem of reduced gas velocity due to pressure drop ahead of the orifice. However, these valves all use a solid metering pin in the outlet orifice which can produce a non-circular gas jet that may not provide for optimal combustion and maximum turndown.
U.S. Pat. No. 5,238,398 discloses a gas modulating valve for use with a gas burner. The valve accomplishes modulation through the use of two sliding plates positioned next to each other that have orifice holes that result in a reduced orifice passageway when the two plates are misaligned with each other. One of the two variations disclosed discharges a gas jet directly into the mixing tube of a gas burner, while the second variation operates as an in-line gas modulating valve. However, due to the nature of the two sliding plates, the gas discharge jet issuing from the variable orifice is neither perfectly centered in the mixer tube of the burner, nor is it perfectly round in cross-section.
Gas Research Institute, which owns U.S. Pat. No. 4,930,488 (the '488 Patent), was exceptionally skilled in the art and likewise did not find adequate teaching or motivation in the prior art to develop a gas modulating valve using the metering pin method operating at the outlet orifice as a method of modulating the fuel flow into the burner to solve a significant need in the industry. They were specifically tasked with a project to develop a microprocessor controlled temperature control system, citing significant needs in the industry. Specifically, “ . . . the lack of an inexpensive and reliable microprocessor controllable gas valve . . . ” where “ . . . modulation of the gas flame has the advantage of tighter control of temperature . . . ” In addition “ . . . there is a need for gas flame modulation as well as enhanced functionality of the range.”
As a pure research company representing the gas (including appliances) industry, one of their objectives was to develop a system that could be competitively manufactured and marketed for use in the gas industry. In addition, one of their guiding principles is to save gas through the development of improved, more efficient gas controls.
Gas Research Institute developed a solenoid operated modulating valve, having a flat seal operating on a valve seat just ahead of the outlet orifice. This ‘free-floating’ design is known to exhibit ‘hunting’, a condition where the valve will repeatedly close and open at a certain proximity of the valve to the exit hole. The condition can be seen illustrated in the displacement vs. current chart in FIG. 4 of the '488 Patent. The chart shows a ‘gap open’ from nearly zero to 0.06 inches. This is due to the coil force overcoming the force of the pressure differential across the closed valve and seat (exit), and then the spring pressure ‘jerks’ the valve further open once the valve breaks free from the seat and the pressure differential rapidly diminishes. The opposite will occur on trying to adjust to a low flow rate. As the valve approaches the seat, the velocity of the fuel flow and the increasing pressure differential will at a certain point ‘jerk’ the valve closed. This type actuator is incapable of modulation at low flow rates, thus there still remains ‘a need’ for an improved modulating valve as outlined in the application.
This type of device for positioning is well known in the art, and is known to exhibit excessive hysteresis and non-repeatability. This “hysteresis in the setting behavior” is specifically cited in U.S. Pat. No. 6,287,108 Rothenberger (col. 1, line 45) as a problem in the prior art leading to a need for that invention. In addition, there are numerous known customer complaints regarding gas modulating valves and regulators using such type solenoid positioning devices due to the non-repeatability during operation.